Studies on bacteriophage T4 have elucidated many aspects of DNA replication, gene control, and the morphogenesis of a complex multicomponent organelle. But as many questions are raised as have been answered. Of interest to us in these investigations is the mechanism by which a long, concatemeric DNA molecule is ma@ured to a highly condensed, encapsulated molecule of precisely defined length. We view the maturation of T4 as a model system for studying the formation of DNA viruses of higher cells and even perphaps the condensation of the chromosomes of higher cells. Specifically, we ask what is the nature of the DNA/DNA interactions and DNA/protein interactions that guide the DNA molecule into the maturing phage head and mediate its proper scission. Currently, we are attacking this problem by studying the roles of genes 16, 17, 49 and 31 in the formation of the phage head and the time and extent with which the various intermediate structures are associated with DNA.